1. Technical Field
The present invention generally relates to pneumatic tires and devices for monitoring the conditions of the tires. More particularly, the present invention is related to a radio frequency active monitor assembly that is housed in a protective body that is placed in a tire and is free to move about while the tire is in use with nothing connecting the monitor assembly to the tire or tire rim. Specifically, the present invention relates to a monitoring device for a pneumatic tire that is housed in a substantially spherical protective body. The spherical body is placed loosely between a tire and a tire rim when the tire is mounted on the tire rim and allowed to freely move about the inside of the tire.
2. Background Information
Monitoring conditions of pneumatic tires while they are installed and in use on a particular vehicle is desired in the art. The users of this technology particularly desire to measure the internal temperature and internal pressure of a tire. These measurements are preferably capable of being taken while the tire is in use without having to remove the tire from the vehicle or otherwise interrupt the use of the vehicle to take the measurements. It is particularly desirable to monitor the conditions and statistics of large off-the-road truck tires because the off-the-road tires are expensive and subject to harsher conditions than typical passenger car tires. The off-the-road tires on large trucks and other vehicles must be regularly maintained to maximize vehicle and tire efficiency.
Numerous types of monitoring devices are known in the art. One type of known monitoring device uses a passive integrative circuit embedded within the body of the tire that is activated by a radio frequency transmission that energizes the circuit by inductive magnetic coupling. Other prior art devices used for monitoring tire conditions include self-powered circuits that are positioned external of the tire, such as at the valve stem. Other active, self-powered programmable electronic devices are disclosed in U.S. Pat. Nos. 5,500,065, 5,573,610, 5,562,787, and 5,573,611 which are assigned to the Assignee of the present application.
One problem common to each of these monitoring devices is the problem of attaching the monitoring device to the tire with a stable and lasting attachment. The attachment problem is difficult when the monitoring device is attached to the inside of the tire, the outside of the tire, or embedded within the body of the tire. The mounting configuration must maintain the integrity of the tire. Mounting the device to the rim also creates problems. The rim may be damaged, a tool must be created, and the mounting configuration must prevent air from leaking from the tire. Each of these locations creates different problems with the attachment process as well as the manufacturing process of the tire. It is generally undesirable to provide an attachment configuration that requires re-tooling or any re-directing of the existing tire manufacturing lines. It is thus desired in the art to provide a monitoring device for a pneumatic tire that obviates the attachment problems inherent with the prior art monitoring devices.
The prior art attachment problems exist because the engineering strains on an electronic monitoring device while connected to a pneumatic tire are significant and frequent. The forces in the footprint area of the tire must be considered when mounting a monitoring device. Tires are subject to rotational forces when the vehicle is moving and also to various impact forces when the tire contacts bumps or surface irregularities. The attachment of the monitoring device to the tire must be strong enough and secure enough to maintain the position of the monitoring device with respect to the tire while experiencing all of these forces while also protecting the monitoring device from damage resulting from these forces. These concerns have lead to the encapsulation of the monitoring devices and numerous methods of attaching the monitoring device to the internal wall of a tire.
The attachment of the monitoring device to the internal wall of the tire requires the tire to be balanced about its rotational axis prior to use. The monitoring device itself adds weight to the tire and the attachments known in the art add further weight to the tire requiring the tire to be counterbalanced. It is thus desired to provide a monitoring device that may be used with a tire without requiring the tire to be counterbalanced.
Another significant problem experienced with attaching a monitoring device to a pneumatic tire is that the surface of the tire where the monitoring device is typically anchored is not stable. Tires are designed to flex and stretch to accommodate various internal pressures and external and internal forces. The attachment of the monitoring device to the tire must accommodate the movement and stretching of the tire surface where the monitoring device is connected. Such accommodation must last throughout the life of the tire and function at a wide range of temperatures and pressures. It is thus desired in the art to provide a monitoring device that may be used with a pneumatic tire without being connected to one of the tire surfaces that flexes and stretches.
Another problem in the art is that off-the-road tires typically have water or another liquid in the bottom of the tire. One type of liquid typically placed in tires is a sealant sold under the Federally Registered Trademark Tire Life by Fuller Bros., Inc. of Portland Oreg. The monitoring device of the invention must be able to operate in a wet environment. Monitoring devices submerged in a liquid will likely have impaired transmission performance and data may be lost because of the position of the device in the tire.
In view of the foregoing, it is an objective of the present invention to provide a monitoring assembly for a pneumatic tire that may be monitored from the outside of the tire while the tire is mounted on a tire rim and while the vehicle is in use. The invention provides a monitoring assembly for a pneumatic tire that is placed within the tire but is not connected to the tire or tire rim allowing the monitoring device to move about freely inside the tire.
The invention provides a monitoring assembly for use in a pneumatic tire having at least one sensor for detecting an engineering condition of a tire, a body surrounding the sensor, and a device that orients the body of the monitoring device in a predictable manner when the monitoring assembly is disposed in a liquid. In one embodiment of the invention, a mass is positioned to cause the sensor (or the tube leading to the sensor) to be positioned at the top of the monitoring assembly so that it is out of the water when the monitoring assembly is floating.
In another embodiment, the invention provides a monitoring assembly that includes a mass that positions the body of the monitoring assembly in a predictable manner so that the antenna is disposed in a predictable configuration with respect to the tire sidewall.